1. Field of the Invention
The present invention relates generally to a television receiver, and more particularly, to a digital television receiver (TV) that can receive both an analog video signal and a digital video signal.
2. Background of the Related Art
Up to now, diverse types of analog TVs from small-sized models of 14 inches to projection TVs of over 60 inches have been presented to consumers.
However, such analog-type TVs have exposed various kinds of problems as they become large-sized and have high-grade functions.
First, in case of viewing the existing analog-type broadcasts such as an NTSC, PAL, or SECAM type through a large-sized TV, it can be known from experience that the picture quality deteriorates.
Second, the number of serviceable broadcasting channels in a channel range of both a very high frequency and an ultra high frequency, which are currently allocated to the TV broadcasts, is limited to about 80, and the number of actually useable ground wave channels is only a half thereof due to the interference among adjacent channels.
Third, the analog-type TV has limitations of a unidirectional medium.
Specifically, the existing TV has only the function of a receiving medium, but from now on, it requires the function of a bidirectional terminal as the demand for the bidirectional function is tremendously increasing with the appearance of personal computers, Internet and so on.
Last, the market for analog TVs is at its peak of congestion.
In other words, since over two TVs have now found for a household in this country, no more demand therefor can be expected.
As a result, digital TVs have appeared as a scheme for solving the above problems in the analog TV market. The digital TV provides a clear picture quality over twice as high as that of the analog TV by greatly improving the picture quality of the analog TV. Also, since no interference exists among the adjacent channels, all the channel regions that could not be used in the existing analog TV can be used.
Also, according to the program service information protocol (PSIP) that is the standard, which is related to broadcasting additional information for providing detailed information on broadcasting programs, among the Advanced Television Service Committee (ATSC) that is the United States digital TV standards proposed in November 1997, one high definition (HD) digital broadcasting program or four standard definition (SD) digital broadcasting programs can be transmitted for a physical channel of 6 MHz, and thus the digital TV has the advantage in that it can provide several hundreds of diverse services. Also, since the digital TV is bidirectional and provides services such as Internet services, home shopping, home banking, etc., it has a great possibility that the analog channels are replaced by the digital channels sooner or later, and thus the tremendous demand for the digital TVs is expected.
However, in order to change the current analog ground wave broadcasting system to the digital ground wave broadcasting system, all the broadcasting equipment and TVs should be changed, and this requires a lot of time. Thus, the analog ground wave broadcasting system and the digital ground wave broadcasting system are in coexistence for a given period of time, and the digital TVs combined with the analog type, which can receive both the analog ground waves and the digital ground waves, are commercialized until the digital broadcasting system is completely established.
The conventional digital TV combined with the analog type, as shown in FIG. 1, includes a first NTSC tuner 12 and a second NTSC tuner 13 for selecting broadcasting signals of specified analog channels, an ATSC tuner 14 for selecting broadcasting signals of specified digital channels, an RF switch 11 for being connected to one among the first NTSC tuner 12, the second NTSC tuner 13, and the ATSC tuner 14 according to a user's selection of a channel or a main/sub picture, and receiving an RF signal of the corresponding channel through an antenna, an audio processing section for processing an audio signal of the broadcasting signal selected from the first NTSC tuner 12 or the second NTSC tuner 13, and outputting the processed audio signal to a speaker 21, a video processing section 16 for processing the broadcasting signal selected from the first NTSC tuner 12 or the second NTSC tuner 13, and outputting the processed video signal to a display section 22 such as a CRT, a SAW filter 17 for filtering a desired frequency band of the broadcasting signal selected from the ATSC tuner 14, an IF demodulating section 18 for demodulating video and audio IF signals from an output of the SAW filter 17, a VSB decoder 19 for decoding an output of the IF demodulating section 18, a mixer 20 for mixing an output of the video processing section 16 and an output of the VSB decoder 19, and the display section 22 for displaying an output of the mixer 20 on a display screen.
At this time, the first and second NTSC tuners 12 and 13 are analog tuners of the NTSC type currently adopted in this country among the analog broadcasting types of NTSC, PAL, SECAM, etc. The ATSC tuner is an ATSC digital broadcasting type filter adopted in this country.
The operation of the conventional digital TV combined with the analog type as constructed above will be explained.
For example, if a user selects a main/sub picture in a state that images of the main and sub pictures are all analog images, a channel broadcasting signal corresponding to the main picture is selected by the first NTSC tuner 12, and a channel broadcasting signal corresponding to the sub picture is selected by the second NTSC tuner 13 under the control of a microcomputer (not illustrated) that has recognized the user's command.
The main-picture and sub-picture broadcasting signals selected by the first and second NTSC tuners 12 and 13 are then processed by the video processing section 16, synthesized, and displayed through the display section 22.
Meanwhile, if the user selects a digital broadcasting channel, the corresponding channel broadcasting signal is selected by the ATSC tuner 14, and then processed through the SAW filter 17, the IF demodulating section 18, and the VSB decoder 19.
At this time, if the user selects the analog video signal for the main picture or the sub picture, the main-picture or sub-picture analog video signal outputted through the first or second tuner 12 or 13 and the video processing section 16 is outputted to the mixer 20, and mixed with a digital image outputted from the VSB decoder 19 in the mixer 20. The mixed image is then displayed through the display section 22.
Accordingly, if the user selects the analog channels for the main and sub pictures, two analog tuners are required for implementing the corresponding images. Also, in case of the digital channel, a separate digital tuner is required. Thus, three tuners are required in total.
As a result, the conventional digital TV that has the main/sub picture function requires three tuners including two analog tuners and one digital tuner, and this causes the manufacturing cost of the TV to be increased.